The present invention relates to a method of and an arrangement for producing bags, sacks or similar objects of a thermoplastic synthetic plastic foil web. The present invention also relates to bags, sacks or similar articles as well as to a synthetic plastic foil web and a foil strip with printing marks for their production.
It is known to produce bags, sacks or similar objects of a thermoplastic synthetic plastic foil web by welding and separating the latter, in acordance with which these steps are controlled by printing marks provided on the synthetic plastic foil web. The printing marks are sensed by photoelectric control or similar devices for controlling the welding and separation. Synthetic plastic foil webs, bags, sacks or similar objects, and foil strips with printing marks are also known in the art. Bags, sacks, or similar objects produced from a thermoplastic synthetic plastic foil are printed in many cases. The printing is performed at the end of the production of the synthetic plastic foil web in an extruder, mainly after the blowing process. In many cases multiple color printing is used. With such color synthetic plastic foils webs it is necessary to arrange the color imprints on the finished bag, sack or similar object, always at the same location, for example so that they are arranged at a predetermined distance from the upper and lower edges.
For achieving this, printing marks are attached to the foil web with its printing. They are controlled by photoelectrical means or similar devices so as to provide a proper alignment of the printing image on the finished bag or sack. With the aid of the printing marks also the local position and the time of processing is controlled, so that for example, the longitudinal and transverse weldings with the separating cuts, or also the fitting steps and providing of the closing seam are achieved on the correct location.
For printing the thermoplastic synthetic foil web, a preceding electronic processing is required. This electronic processing reduces the capability for welding of the foil web. When the foil web starts from a hose or a cut hose and then forms from a flat web, and then the hose is provided with side folds, the electronic processing interferes with the welding in the region of the side folds.
Synthetic plastic foil web processing machines for producing bags, sacks or similar objects are provided with photoelectrical control devices or similar electronic devices which control printing marks attached by printing of the foil web and respectively determine nonmechanically the length of the bag, sack or similar object. Thereby these machines are not suitable for processing non-printed foil webs.
On the other hand, there are bags, sacks or similar objects from non-printed foils which require certain distances inside the bag for controlling the welding and separating device, for example the distance of a gripping opening from a filling opening or a transverse welding. For maintaining these distances with the required safety it was necessary to print printing marks on the foil web. The printing of the printing marks, however, requires, even in a small region, the electronic processing of the foil over its entire length, wherefore a significant labor is needed. Such a synthetic plastic foil web which is electronically processes and provided with printed printing marks is limited in its use, since the distances of the printing marks from one another and their distance from the edge of the foil web can be used only for certain formats of bags or sacks.